Well, I had this problem awhile ago with windows messenger after some windows updates.  I did uninstall and go back to an earlier version but I missed windows live messenger.  I looked around and on a forum I found that one windows update messed up the registry settings.  There was a utility I downloaded and it cleaned out the settings in question.  I wished I had done that earlier because I lost some of the graphics I had been using.  I don't know if this is your problem or not.  I'll try and find that site again.  In the meantime, trillian will work if it is the same problem.  Its good for a fall back utility.